1. Field of the Invention
The present invention relates to an electric terminal member and also to a coil assembly utilizing such terminal member.
2. Description of the Prior Art
Electric wires largely employed in practice are generally made of copper. However, aluminum has a good electroconductivity and inexpensive as compared with copper and, accordingly, if aluminum is used for electric wires and/or coil windings, some advantages can be appreciated.
Even though the electric wires or coil windings are made of aluminum, it is not infrequently required for those electric wires or coil windings to be electrically welded or soldered to existing electric terminal members or wires made of copper. However, by the reasons which will be described subsequently, soldering of the aluminum wires or coil windings to the copper based terminal member or wires has generally considered difficult to achieve.
In the first place, when a soldering material of a copper-tin system is used in connecting an aluminum wire electrically with a copper wire, electric erosion tends to occur in the aluminum wire due to the potential difference which will develop when the circuit including the aluminum wire connected with the copper wire is in use. Also, if a soldering material of a zinc-tin system is used for the same purpose, an oxide layer tends to be formed on the surface of the aluminum, which leads to a rejection of the soldering material used. Although a method has been contemplated, in which soldering is performed under a vacuum atmosphere in order to avoid formation of the oxide layer referred to above, this method is so costly as to render it remote from the practical utilization.
Another method has been suggested, in which in order for a soldered connection to be achieved between the aluminum conductor and the copper wire, a copper plated layer is continuously formed by means of a copper electroplating process on an outer surface of the zinc layer, which has been formed on the surface of the aluminum conductor by means of a zinc substitution process. See, for example, the Japanese Laid-open Patent Publication No. 2001-271198, published Oct. 2, 2001, which discloses a copper coated aluminum wire. It has, however, been found that this technique requires the use of a complicated electroplating process.
In addition, where in order to remove the oxide layer on the aluminum surface, a flux is applied to the aluminum surface prior to soldering by dipping, immersion of aluminum into a soldering bath causes an abrupt increase of the temperature, resulting in scattering of the applied flux. This leads to such a problem that no soldering can be achieved successfully.